In wireless communications at different times there may be different data transmission needs for a wireless device, e.g., in terms of amounts of data, type of data, range, intended recipients, acceptable bit error rate, etc. In addition, at different times, the desired transmission power level may be different, e.g., as a function of the type of communications channel, type of data, current channel conditions and/or interference conditions. In some wireless communications systems, transmission signal characteristics may vary as a function data transmission needs and/or desired transmission power level, e.g., during some times a multi-tone signal may be generated and transmitted while at other times a single tone signal may be generated and transmitted.
Generally, it is desirable to use linear amplifiers in communications systems since they do not introduce unwanted harmonics into a signal being amplified. Such harmonics can be particularly difficult to filter out in the case of multi-tone signals since attempts to filter out the effects of the use of a non-linear amplifier on a signal can often negatively impact one or more of the tones which are to be maintained in the signal being amplified.
In the case of wireless communications devices intended for the consumer market, e.g., cell phones and other mobile devices, issues of both cost and power consumption are of concern. Amplifiers which are linear over a wide power range tend to be expensive particularly if they are designed to be linear for a range of frequencies as opposed to a single frequency. Accordingly, it can be cost prohibitive in many applications to use linear amplifiers where a broad range of power outputs are to be supported. In addition to cost issues, non-linear amplification can have power efficiency advantages over linear amplification techniques making non-linear amplification desirable in devices, e.g., hand held devices, where power efficiency is of concern.
While it can be beneficial to use non-linear power amplification in some situations, non-linear power amplification is not well suited for multi-tone signal transmissions due to the interference issues associated with non-linear amplification of multi-tone signals. Thus, despite cost issues, many wireless communications devices, implemented to support the use of multi-tone signals, use linear power amplifiers for their pre-transmission power amplification operations.
Based on the above discussion there is a need for methods and/or apparatus which would allow wireless communications devices to use non-linear amplification, under at least some circumstances, without significant negative impact on the use of multi-tone signals by a device during at least some periods of device operation.